nvmem: u-boot-env: use nvmem device helpers

nvmem: u-boot-env: use nvmem device helpers

[ Upstream commit a832556d23c5a11115f300011a5874d6107a0d62 ]

Use nvmem_dev_size() and nvmem_device_read() to make this driver less
mtd dependent.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20231221173421.13737-4-zajec5@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 8679e8b4a1eb ("nvmem: u-boot-env: error if NVMEM device is too small")
Signed-off-by: Sasha Levin <sashal@kernel.org>